Subscription television systems can be cable television systems (CATV), multi-point, multi-distribution subscription systems (MMDS), direct-to-home (DTH) broadcast or satellite systems. The sophistication of communications systems involving subscription television is continually increasing. While providing transmission signal quality satisfactory to even the most persnickety viewers, systems currently installed have greatly improved communications capabilities and facilitate a wide variety of business arrangements between the subscriber and the system operator. For example, such features as impulse-pay-per-view, various conditional access schemes, addressable messaging systems and other text services, and electronic programming guides, to name just a few, may be supported.
In order to provide and enable operator control of such services, a multitude of apparatus is required. As a result, subscription television systems have become increasingly complex. For example, the subscriber terminals have conventionally provided the functions of tuning particular channels of the subscription system which are outside of the subscriber's television receiver capability. Further, they provide conditional access to particular subscription service through authorization of particular channels of service by descrambling.
More recently, the subscriber terminal has become user friendly by providing an interactive, on-screen display and other user functions that allow the subscriber to manipulate the cable service and his television receiver in additional ways. These features include volume control, sleep timer features, parental control capabilities, program timers for recording programs on a video cassette recorder (VCR) and other types of consumer-friendly operational features.
An advantageous example of a subscriber terminal with advanced consumer features is the Model 8600 series of subscriber terminals manufactured by Scientific-Atlanta, Inc. of Norcross, Ga. These terminals generally provide on-screen displays by combining the video signal from a selected channel with an on-screen display video signal from a video generator prior to remodulation of the combination to either Channels 3 or 4. In addition, a more sophisticated example of an on-screen display in a subscriber terminal is discussed in U.S. patent application Ser. No. 08/073,404, filed Jun. 7, 1993, entitled "Display System for a Subscriber Terminal", which is incorporated herein by reference.
Despite the recent advances, there remains a general need to provide new and additional services and features to satisfy the eclectic tastes of subscribers. In addition, there is a need to make existing systems even more user-friendly. Further, there is a need to provide a variety of services without increasing bandwidth requirements. In conventional subscription television systems, a broadband television signal having a plurality of 6 MHz frequency channels is generated at a headend and transmitted via a distribution system to subscriber terminals. Each of the 6 MHz frequency channels includes video and audio information corresponding to a discrete television (TV) program. Accordingly, to transmit four TV programs, for example, 24 MHz of bandwidth is required. When the user selects a service channel for viewing, the subscriber terminal tunes to the corresponding frequency channel, and video and audio information associated with the selected service channel is displayed.
Multi-service communications systems transmit different services over one or more different frequency channels thereby providing additional service without a corresponding increase in transmission bandwidth. Each frequency channel may carry text services in addition to video and audio information that compose a standard TV service. Therefore, to gain access to a text service, a subscriber terminal must have information to tune to the frequency channel carrying the text service and information to select the desired text service from the several text services and the TV service provided on that frequency channel.
U.S. Pat. No. 4,908,859 to Bennett, entitled "Receiver Access Interface to Service Components in Television Channel" discloses a receiver interface system that stores a service definition table, a service-to-channel map, and a channel configuration map. The service definition table defines the relation between service components and service numbers. The service-to-channel map defines the relationship between service numbers and interface channel numbers. The channel configuration map defines the relationship between frequency channels and interface channel numbers. Using these relationships, a receiver can locate and access a service selected by a user in signals transmitted over various frequency channels.
U.S. Pat. No. 5,200,823 to Yoneda et al., entitled "Virtual Channels for a Multiplexed Analog Component (MAC) Television System", contains a description of a television system for providing services, including video, audio, and text services, to remotely located subscribers over a plurality of channels. A decoder at the subscriber location receives audio, video, and text components over each physical channel. The decoder contains a mapping of each physical channel to virtual channel numbers. Each virtual channel may use a different combination of components. For example, one virtual channel may comprise linked pages of text service. A user can select a virtual channel using a selector and thereby receive the combination of service components defined by the virtual channel.
Many viewers desire to view multiple services simultaneously. In addition, subscription television operators recognize the benefits of providing multiple services simultaneously to subscribers. One known solution is to provide subscribers with two subscriber terminals in a master-slave relationship. The subscriber terminals may be linked to each other via a serial data port or other information connection. The incoming cable carrying the broadband television signal is input to an RF splitter having outputs to each of the master and slave subscriber terminals. All control functions can be performed by the master subscriber terminal. For example, the master subscriber terminal may be used to control the tuner of the slave subscriber terminal. The user can control the tuners in each subscriber terminal to tune to the different frequency channels which carry the two programs that the user wishes to view.
For example, the output of the subscriber terminals is supplied to a picture-in-picture capable television set. Accordingly, the user can view two different programs simultaneously. This arrangement would, in addition, allow a user to record one program selection on a VCR or like recording device while simultaneously viewing another program selection simply by connecting the output of one of the subscriber terminals to the recording device.
However, it is expensive for each subscriber to purchase or lease two subscriber terminals. In addition, providing the information to support two services on separate channels reduces the bandwidth available for other purposes. Accordingly, there is a need to enable subscribers to view multiple programs simultaneously without increasing the transmission bandwidth.